The present invention relates to the demodulation of digital ON-OFF-keyed (OOK) and phase shift keying (PSK) signals, and particularly to a method and apparatus for producing a zero-valued intermediate frequency (IF) by a frequency-controlled loop in a phase-diversity receiver for demodulating received OOK and PSK signals.
Establishing a coherent reference signal is a crucial requirement in homodyne FM receivers. With relatively stable frequency sources this can be achieved by locking one phase of a local oscillator to the phase of the signal carrier--or if modulation is such that the carrier is not suppressed, to that of the virtual carrier. When local oscillators are not sufficiently stable for such phase-locking, the technique of phase-diversity reception is often used; for then, only the frequency of the local oscillator need be controlled, and diversity combining is effectuated in order to compensate for the lack of phase coherence.